Ultrasound imaging has been employed for various medical applications. Methods of improving imaging performance in such cases are of general interest. One method of improving ultrasound imaging is the use of microbubbles as contrast agents. For example, microbubbles can be configured to specifically bind to tumor antigens to aid in cancer detection. However, new problems can arise in connection with the use of microbubbles as contrast agents. In particular, if it is desired to have the microbubbles remain intact during imaging (as opposed to the more conventional approach of bursting the microbubbles when imaging), then it is necessary to have a relatively low incident acoustic intensity, which undesirably tends to reduce image quality. Accordingly, it would be an advance in the art to provide improved acoustic imaging using microbubbles as contrast agents.